A human whole blood model of LPS-mediated suppression of T cell activation.

Background: Lipopolysaccharide (LPS) is the main initiator of the early signaling events leading to sepsis caused by Gram-negative bacteria. Late stages of sepsis are associated with impairments of T lymphocyte function, a condition associated with nosocomial infection and poor outcome. The molecular basis for septic immunosuppression is not fully understood.
Material/methods: Human whole blood was incubated ex vivo with purified LPS. Cytokine responses and T cell proliferation were assessed, and the role of cyclic 3',5'-adenosine monophosphate (cAMP) in T cell suppression by LPS was studied using a cAMP-antagonist (Rp-8-Br-cAMPS).
Results: Adding LPS (0.01 to 10 microg/ml) to human blood ex vivo caused a release of prostaglandin E2 (PGE2) in a concentration- and time-dependent manner, with maximal levels of PGE2 obtained with 10 microg LPS per ml blood after 10 hours of incubation. Adding PGE2-concentrations ranging from 0.03 to 10 microM to purified T cells completely abrogated T cell activation and proliferative response, which was largely reversed by adding Rp-8-Br-cAMPS. Peripheral blood mononuclear cells (PBMC) and T cells harvested from whole blood cultured in the presence of LPS ex vivo showed attenuated proliferative response (30-70%) (purified T cells and PBMC) and reduced IL-2 production (85%) upon T cell receptor (TCR)/CD3 activation with anti-CD3. The proliferation in T cells and PBMC was in part restored by Rp-8-Br-cAMPS.
Conclusions: The human whole blood model of LPS-mediated T lymphocyte suppression described in this paper is time and cost efficient, as well as easy to use.